Former Tranmere Rovers skipper Clint Hill blasted his first goal for Oldham and sent his old club crashing to their first defeat of the season.
Hill was Tranmere's star man last term but turned down a contract in the summer and was on his way for £225,000, but he showed little mercy to grab the man of the match award and leave Rovers' manager Ray Mathias scratching his head.
Mathias said: "I don't remember Clint scoring many goals like that before, I'm sure he never did it when he played for us.
It was a good one but our marking was sloppy because he got above two defenders.
"The script was written for him and I was disappointed with the manor of the goal because we had been coping quite well. But we will pick ourselves up no problem because we were unbeaten in our three games before this."
Oldham's first home win was achieved with their third consecutive clean sheet and new boss Iain Dowie said: "That's what pleases me most. We work very hard on our defending and Tranmere hardly ever looked like scoring."
The visitors' best chance fell to Jason Price whose control was poor as he bore down on giant Aussie goalkeeper Les Pogliacomi.
Jason Koumas did his best to prompt more football but the sought after midfielder was eventually crowded out of his game by Oldham's tight marking.
Oldham had a couple of openings wasted by Chris Killen before Hill had his moment midway through the second half.
He thumped in a header from 10 yards, a goal which saw Oldham take over.
The second came after 77 minutes when debutant Clyde Wijnhard volleyed in powerfully from eight yards after Carlo Corazzin's flick.
Wijnhard is looking for a permanent contract at Boundary Park and the fans who gave the ex Leeds star a standing ovation were certainly impressed